Deepwater managed pressure drilling (MPD) can include a number of different types of field operations, including but not limited to sea floor mud lift drilling (SMD) (also called other names, such as subsea mudlift drilling). SMD can exist in at least two different configurations, including but not limited to single gradient drilling (SGD) and dual gradient drilling (DGD). In the DGD variation, SMD is used in deep water field operations where the drilling mud is pumped from the sea floor to the drilling vessel to create the effect of dual pressure gradients in the returning mud column. When SMD is used with a conventional marine riser, the riser is filled with seawater, and the mud is pumped up return lines. When used with independent return lines, the SMD system permits “riserless” drilling, which refers to lack of a conventional marine riser. Smaller return lines require much less tension, may be faster to deploy, and contain much less mud volume.